1. Field of the Invention
The invention relates to a planetary gearset and an automatic transmission, and particularly to a planetary gearset and an automatic transmission provided in a vehicle in which enable the periphery of each pinion gear of the planetary gearset to be appropriately lubricated when the carrier of the planetary gearset is not rotating.
2. Description of the Related Art
In general, an automatic transmission for a vehicle includes a planetary gearset having: pinion gears that are provided between and mesh with a sun gear that is rotatable about the rotational center shaft and a ring gear that is provided on the radially outer side of the sun gear; and a carrier that has pinion shafts on which the pinion gears are rotatably supported via corresponding bearings, respectively, and which is rotatable about the rotational center shaft.
Because, in such a planetary gearset, the mesh area between the respective gears need to be lubricated for smooth rotation of each gear while minimizing the reduction of the durability of each gear, various designs have been developed for appropriate lubrication.
FIG. 12A and FIG. 12B each show the lubrication structure of a conventional planetary gearset (For example, see JP-A-2004-270736). Referring to FIG. 12A, a carrier 2 is rotatable about a rotational center shaft 1 that is coupled with an engine, and the carrier 2 has a pair of annular sidewalls 2a, 2b that are perpendicular to the axial direction of the rotational center shaft 1. Pinion shafts 3 are provided between the sidewalls 2a, 2b such that each of the pinion shafts 3 extends in parallel to the axial direction of the rotational center shaft 1.
A pinion gear 5 is rotatably supported on each pinion shaft 3 via a needle bearing 4. The pinion gears 5 are arranged between a sun gear 6 attached on the outer periphery of the rotational center shaft 1 and a ring gear 7 provided on the radically outer side of the sun gear 6, such that the pinion gears 5 mesh with the outer periphery of the sun gear 6 and the inner periphery of the ring gear 7.
Within each pinion shaft 3 is formed an axial oil passage 8 that extends in the axial direction and communicates with the space between the outer periphery of the pinion shaft 3 and the inner periphery of the pinion gear 5 via a through hole 9 extending in the radial direction of the pinion shaft 3. The lubricant that is guided into the axial oil passage 8 is supplied via the through hole 9 to the needle bearing 4 and to where the pinion gear 5 meshes with the ring gear 7. A guide plate 10 is integrally provided at the sidewall 2a, which guides lubricant into the axial oil passage 8.
The guide plate 10 is annular and intimately attached to the sidewall 2a so as to be coaxial with the rotational center shaft 1. The guide plate 10 is grooved such that a guide passage 11 is formed between the guide plate 10 and the sidewall 2a. As shown in FIG. 12B, the guide passage 11 is formed like the letter “S” as a whole, having: an intermediate passage 12 that extends straight in an oblique direction between the inner peripheral side and the outer peripheral side of the guide plate 10 across the inlet of the axial oil passage 8; a first guide portion 14 that extends straight towards the inner peripheral side from a first curve 13 that is a sharp curve at the outer peripheral side end of the intermediate passage 12; and a second guide portion 16 that extends straight towards the outer peripheral side from a second curve 15 that is a sharp curve at the inner peripheral side end of the intermediate passage 12. Being thus formed, the opening of the first guide portion 14 is located at the inner peripheral side of the axial oil passage 8 and the opening of the second guide portion 16 is located at the outer peripheral side of the axial oil passage 8.
In the guide passage 11 formed as descried above, when the automatic transmission is at a speed at which the carrier 2 is driven to rotate, lubricant moves towards the outer peripheral side due to centrifugal force and enters the first guide portion 14. This lubricant is then received by the first curve 13, is guided into the axial oil passage 8 from the intermediate passage 12 and flows out from the through hole 9, thus lubricating the needle bearing 4 and the mesh area between the pinion gear 5 and the ring gear 7.
For example, lubricant is supplied from an oil pump into an axial oil passage formed in the rotational center shaft 1, and the lubricant then moves from the rotational center shaft 1 towards the outer peripheral side due to the centrifugal force generated by the rotation of the rotational center shaft 1 and the centrifugal force generated by the rotation of the carrier 2.
Meanwhile, when the automatic transmission is at a speed at which the carrier 2 does not rotate, the lubricant, due to its own weight, flows down into the first guide portion 14 or into the second guide portion 16 and then flows into the axial oil passage 8 through the intermediate passage 12. Then, the lubricant flows out from the through hole 9 and lubricates the needle bearing 4 and the mesh area between the pinion gear 5 and the ring gear 7.
That is, at the pinion gear 5 that is standing still above the rotational center shaft 1, the lubricant, due to its own weight, flows down into the opening of the second guide portion 16 that is facing upward at this time, and the lubricant is then received by the second curve 15. Thereafter, the lubricant flows through the intermediate passage 12 and enters the axial oil passage 8, so that the pinion gear 5 is lubricated. On the other hand, at the pinion gear 5 that is standing still below the rotational center shaft 1, the lubricant, due to its own weight, flows down into the opening of the first guide portion 14 that is facing upward at this time, and the lubricant is then received by the first curve 13. Thereafter, the lubricant flows through the intermediate passage 12 and enters the axial oil passage 8, so that the pinion gear 5 is lubricated.
However, in such a conventional lubrication structure for planetary gearsets in which, using the guide plate 10, the lubricant flowing down into the first guide portion 14 or into the second guide portion 16 due to its own weight is guided into the axial oil passage 8 via the intermediate oil passage 12 and then discharged from the through hole 9, it is difficult to supply a sufficient amount of lubricant from each pinion gear 5 to the mesh area between the pinion gear 5 and the ring gear 7.
That is, because the through hole 9 extends in the radial direction of the pinion shaft 3, even if the lubricant flowing down due to its own weight is utilized as descried above when the carrier 2 is not rotating, a sufficient amount of lubricant may not be supplied via the through hole 9 to the mesh area between each pinion gear 5 and the ring gear 7, which is located on the radially outer side of the pinion gears 5. Thus, there is still a room for improvement.
Meanwhile, it is considered that the mesh area between each pinion gear 5 and the sun gear 6 can be lubricated by, for example, supplying lubricant from the rotational center shaft 1 to the mesh areas via an oil passage that is formed so as to extend in the radial direction of the sun gear 6, by utilizing the centrifugal forces generated by the rotations of the rotational center shaft 1 and the sun gear 6.
However, when so many oil passages for guiding lubricant are formed in the planetary gearset, because of the need for supplying lubricant into the many oil passages, the pressure of lubricant supplied from the oil pump to each oil passage becomes relatively low. This makes it further difficult to supply a sufficient amount of lubricant to the mesh area between each pinion gear 5 and the ring gear 7, which is located on the radially outer side of the pinion gear 5, and this may accelerate wear of the pinion gears 5 and the sun gear 6.